The invention relates to atomic layer deposition processes.
Atomic layer deposition (ALD) is an ideal technique for fabricating thin layers requiring precision-controlled nanoscale film thickness. It is a type of chemical vapor deposition (CVD), wherein a film is built up through deposition of multiple ultra thin layers of atomic level controllability, with the thickness of the ultimate film being determined by the number of layers deposited. The source precursor is-adsorbed in a self-limiting process on the substrate surface, followed by decomposition of this precursor to form a single molecular layer of the desired material. Decomposition may occur through reaction with an appropriately selected reagent. Thicker films are produced through repeated growth cycles until the target thickness is achieved. In an ALD process, a substrate with at least one surface to be coated, a source precursor, and any reactant(s), necessary for forming a desired product, and which is capable of reacting with the precursor to form a desired product on the substrate surface, such as a film, liner, layer or other material, are introduced into a deposition chamber. The precursor and reactant(s), both of which are typically in vapor or gaseous form, are pulsed sequentially into the deposition chamber with inert gas pulses in between the precursor and reactant pulses, for a specified, typically predetermined, short period of time, and allowed to react on the substrate surface to form an atomic layer of the desired thickness, typically on the scale of an atomic monolayer.
In practice, the reactant gases are alternately pulsed into the reactor, separated by an inert gas flush. The characteristic feature of ALD is that each reactant is delivered to the substrate until a saturated surface condition is reached. To obtain a self-limiting growth, it is necessary that sufficient reactant reach the substrate, and also that only a monolayer remain after the inert purge. As the growth rate is self-limiting, the rate of growth is proportional to the repetition rate of the reaction sequences rather than to the flux of reactant, as in CVD.
Cobalt-containing alloys are of interest for giant magnetoresistance (GMR) applications. Cobalt is also deposited onto silicon gate contacts in integrated circuits to form cobalt silicide upon annealing. Deposition of cobalt is typically via sputtering, and CVD routes have also been explored. For example, Charles et al., have investigated the metallorganic chemical vapor deposition (MOCVD) of cobalt using bis(acetylacetonate) cobalt(lI), or Co(acac)2, in the temperature range 240-510xc2x0 C. (J. Inorg. Nucl. Chem. p. 995 (1969)). Gu et al. have disclosed use of the same precursor for the MOCVD fabrications of Cu-Co alloys at room temperatures from 250-310xc2x0 C. (Thin Solid Films, 340, p. 45 (1999)).
It has been unexpectedly discovered that a metallic layer may be deposited by an ALD process from a metallorganic precursor, on a noble or semi-noble metal substrate, using hydrogen as a reducing agent. The metal of the deposited layer may be Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, or Au. In one embodiment, the precursor is Co(acac)2.
In another aspect, the invention relates to an atomic layer deposition process which includes depositing a metallic layer on a metal nitride or metal oxide substrate, using an oxidizing agent and hydrogen as a reducing agent. The precursor, reducing agent and oxidizing agent are sequentially pulsed into a reaction chamber containing the substrate, and a purge gas is pulsed into the reaction chamber between each sequential pulse. The metal of the deposited layer may be Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, or Au. In one embodiment, the precursor compound includes a bidentate ligand, for example, a xcex2-diketonate.
In yet another aspect, the invention relates to an atomic layer deposition process which includes depositing, on a substrate, a metallic layer from a metallorganic precursor, using a hydride as a reducing agent. The reducing agent may be, for example, silane. The metal of the deposited layer may be Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, or Au. In one embodiment, the precursor compound includes a bidentate ligand, for example, a xcex2-diketonate. The substrate may have a hydroxyl terminated surface; examples of such substrates include tantalum, silicon, silicon dioxide and fluorinated silica glass.